Users connected with their mobile terminals in a radio network as part of a telecommunications network do not have unlimited use of resources in that telecommunication network. Such is limited by means of policies. Policies may have a general character such as maximum allowed bandwidth for mobile internet upload. These policies are mostly defined by the operator of the telecommunication network and made applicable to all users to allow shared use of services. Policies may on the other hand be part of the subscription. A user having a premium subscription pays more for having more download bandwidth for mobile internet than a user with a regular subscription. This is a typical quality of service (QoS) policy.
Quota control is another area of policies for fair usage control. Charging is used as general term but it also includes quota control. Typical real charging control example is users having a prepaid subscription. When a user makes use of a service in the telecommunication system that has a use dependent charging, that service will reserve credit from the users prepaid account prior to rendering the service. When that credit is used or almost used, again credit is requested by the service. At the end only actual consumed credits are reported back by the service and the remainder is added back to the account. The operator can define as a policy a maximum amount that a service may reserve or a maximum time a credit may stay reserved etc.
Typical example of quota control for fair usage is a user having a subscription that allows maximum 350 Mb per month mobile internet download. Also here a likewise reservation mechanism and subsequent operator policies may be applied.
The above described policies are combined in fair usage control as shown in the table below;
SubscriptionBandwidthQuota limit/typelimitmonthAdditional rulePremium3.6 Mb5 Gb >5 Gb down to 128 Kb/sAll in one  1 Mb1 Gb >1 Gb operator portal onlyregular3.6 Mb350 Mb >350 Mb operator portal only
The additional rules are policies defining what to do if quota is exceeded, alternative for simply deny service. The combination of QoS, Quota, and additional rules is seen as a set of fair usage control policies.
The discussed limitations are generally seen as rules to be applied by the telecommunication system. Many of these rules are stored with other subscription details in a repository with user subscription data like the HLR (Home Location Register) in the GSM system. Operator defined general rules could be added to each subscription but this would make updating a cumbersome task. For that reason the circuit switched type of telecommunication system had already defined a rule repository function where the operator could add overall applicable rules and the subscription based rules were aligned with the subscription repository. The rule repository function combined policies to one set to be applied to a certain user having a subscription in the network. Also already known in the circuit switched type of telecommunication system was that in the end rules must be enforced. Enforcement typically takes place in the dedicated nodes of the telecommunication system where the actual resources are controlled. For that purpose policy or rule enforcement points were defined that included in the nodes or locally connected to the nodes took care of the enforcement of rules in the rule repository.
Evolution in telecommunication systems has its progress and IP based information exchange has been taken as core transport for the telecommunication system. This is commonly denoted as 3GPP packet switched domain or packet core network. At the same time the telecommunication system opens up to allow other non radio access terminals on IP basis. The known circuit switched policy handling was no longer sufficient in an all IP domain. Crucial is that in the packet switched domain there is no longer a dedicated circuit for the user on which policy enforcement can take place. Packets can take a multitude of dynamic routes to their destination. Therefore a new concept on policy control and enforcement was required. 3GPP has started a new standardization for policy/rule handling in 3GPP TS 23.203. This standard shall cover all current packet access technologies like GPRS, LTE, WLAN and Wifi, Docsis etc. for the purpose of Policy and Charging Control (denoted as PCC in the standard).
Like in the circuit switched domain the standard defines a central rule decision function PCRF (Policy and charging rule function) and the decentralized enforcement function PCEF (Policy and Charging Enforcement Function). Further referring to FIG. 1 the 3GPP defined architecture for PCRF and PCEF is discussed.
In absence of a fixed circuit with assigned resources an alternative is needed on which policy enforcement could take place. Starting point is the registration of the user terminal to the access network. User terminal must be seen widely as being a mobile phone connecting to the GSM/UMTS/LTE radio network, a lap top PC connecting via WIFI or WLAN, or a fixed PC via DOCSYS cable system, etc. After registration the user equipment has been assigned an IP address. As part of the registration on the access network also an IP-CAN (IP Connectivity Access Network) session is established. The establishment of the IP-CAN session comprises amongst others the binding of one or more IP-bearers. The IP bearer is a virtual point to point transport channel for packages through an IP network. When the user terminal is connected via radio channel the IP bearer runs from radio access point (radio base station, E-nodeB or WLAN access point etc.) to the gateway. The bearer between radio access point and user terminal is defined as radio bearer. Both bearers are so shared by multiple user terminals. The bearers are intended for transportation of packages related to contents going to or coming from the user terminal (voice, data, internet pages, video etc.). It does not include signalling related to access network registration and control.
As IP bearers are virtual channels they have a planned capacity as part of overall IP transport network capacity planning. When an IP bearer is bound to an IP-CAN session it becomes an IP-CAN bearer from the view point of the IP-CAN session. Part of the binding is an agreement on the quality of service (QoS). Without agreement packages are transported on Best Effort (BE). Instead agreements can be made on the bit rate, error rate, package delay, packet loss rate, etc. Each of these characteristic is denoted as a QoS Class Identifier (QCI). Important example is the bit rate which is agreed as Guaranteed Bit Rate (GBR). Which value is assigned to a QCI is subject of policy control. The application of policy control should be seen as QoS reservation. It shall be noted that the binding of IP bearers to an IP-CAN session is dynamic and can change in time due to specific contents requests of the user. Example is request use of a certain application function (AF) by the user which requires an IP-bearer with a certain QoS. The actual binding is performed by the Bearer Binding Function (BBF) under control of the PCRF. The BBF is an integrated function of the Bearer Binding Enforcement Rule Function (BBERF) and the PCEF.
As described earlier there is a difference between operator defined and general applicable rules and subscriber specific rules. The first category is maintained in the PCRF. The second category is collected by the PCRF from a Subscription Profile Repository (SPR) by means of a request via the Sp interface when a user terminal registers with the access network. The SPR can be any data base function holding Subscriber information containing rules, e.g. HLR or AAA server. The SPR updates the PCRF when any change occurs in the subscription. The PCRF informs the SPR when a user terminal deregisters from the access network. The identification used is depending on the type of access network e.g. the IMSI (ISDN mobile station Identifier), PUI (public user identity), or the like.
Certain rules of the PCRF require continuous enforcement while other rules need to be enforced after a certain event. Events are reported to the PCRF by the ERF (event reporting function). The ERF resides in the BBERF or the PCEF. Also the AF can report events to the PORE In the ERF case the PCRF subscribes for notifications of certain events for a dedicated user. The AF event reporting is to be seen as new or changed requirements to rule enforcement based on user requests for contents.
So far QoS enforcement is discussed as applied in establishing the IP-CAN session and binding of IP-bearers. There are other areas for which rules require enforcement.
One other specific area is packet filtering. Example is the limitation to the operator portal web pages only when quota is exceeded, or operator blocking from illegal download sites. Packet filtering is enforced by the PCEF in the gateway. The PCRF provides the filtering criteria to the PCEF upon user terminal registration or after a reported event.
Last area of policy control is the charging control. This includes both online and offline charging. Offline charging is the generation of charging records (CDR: Charging Data Record) to the offline Charging system (OFCS) by the gateway or application function. Online charging comprises not only money wise credits like for a prepaid account but also includes quota management, hence the more general term credit control. Whether account or quota online charging can be event, time or volume based. Online charging is specific to an IP bearer in an IP-CAN session. So concurrent charging will occur. This means that in time or volume based control credit reservations are made, and remaining credits are returned. Policy rules define items like the maximum reservation amount and maximum time a reservation may be outstanding. Online charging is performed by the OCS and enforced by the PCEF on the gateway.
For further details reference should be made to the 3GPP TS 23.203 and 23.402.
The current standardization has not yet provided a solution on how subscription based quota limits as contained in subscriptions in the SPR can be obtained and controlled by the OCS. A currently proposed solution is that the PCRF performs quota control for fair usage itself based on additional functions and extension of the Gx interface. Full details are provided in 3GPP TS 23.203 CR 0237. This provides an advantage that other rules controlled by the PCRF can be combined with this OCS type of quota control.
For fair usage control the main problem is that it is not defined how it should operate when the terminal is roaming, connected via another (visited) network then its home network. In that case both home and visited network have PCRF and PECF/BBERF functions that need to co-operate. This is best seen with concurrence of operator defined rules. Apart from the operator rule concurrence the visiting terminal can have different connection scenario's to local services and services in the home network. Therefore PCEF can be in either network and yet need to be controlled with a single coherent rule set.